44 DETERMINATION OF SPEED [CH. v, 



and valid arguments the other way; so in 1897 

 J. J. Thomson made a much more serious attack on 

 the whole position. 



He arranged that the magnet should deflect the 

 rays into an insulated hollow vessel, connected with 

 an electrometer and a known capacity, so that the 

 aggregate charge of the cathode ray particles collected 

 in a given time could be measured by the rise of 

 potential observed (cf. Fig. 3). He also arranged 

 that inside the hollow vessel they should fall upon 

 a thermal junction of known heat capacity, con- 

 nected by very thin wires to a galvanometer (acting 

 therefore as a calorimeter), so as to measure their 

 aggregate energy. 



Thus he could make the following simultaneous 

 determinations : 



m 



u 



In these three equations there are four unknown 

 quantities ; but one pair can be treated as a ratio, 

 and another, N, can be eliminated, and thus we get 



2W 



When these brilliant measurements were actually 

 made in the laboratory, the atomic nature of cathode 

 rays was, if not actually disproved, at all events 

 rendered highly improbable ; for their speed was 

 found to be of the order ten thousand miles per 

 second, or even as high as ^ that of light in a 



